Sunday, 10 November 2013

[Sorry I've been absent for so long - lots of stuff happening this year.]

The SOCIETY for POPULAR ASTRONOMY

Electronic News Bulletin No. 364 2013 November 10

Here is the latest round-up of news from the Society for
PopularAstronomy. The SPA is Britain's liveliest astronomical society,
withmembers all over the world. We accept subscription payments
onlineat our secure site and can take credit and debit cards. You can
joinor renew via a secure server or just see how much we have to offer
byvisiting http://www.popastro.com/

ASTEROID
2013 TV135NASA

The
then-undiscovered asteroid 2013 TV135 made a close approach tothe Earth on
Sept. 16, when it came within about 6.7 million km. Theasteroid is
estimated to be about 400 m across and its orbit carriesit out to about
three quarters of the distance to Jupiter. It wasdiscovered on 2013 Oct. 8
by astronomers working at the CrimeanAstrophysical Observatory in Ukraine.
It is one of more than 10,000near-Earth objects that have been discovered.
With only a month ofobservations for an orbital period of almost four years,
its orbit isstill poorly determined, but it looks as if the asteroid could
be backin our neighbourhood in 2032. The object will be in the
accessiblepart of the sky in the coming months, and the refinement of the
orbitis likely to show that there is no risk of Earth impact in 2032.

EXOPLANET
TALLY ABOVE 1,000BBC News

The
number of observed exoplanets now stands informally at 1,010,bolstered by 11
new finds from the UK's Wide-Angle Search for Planets(WASP). The Kepler
space telescope, which discovered many suchplanets in recent years, broke
down earlier this year, but it left alist of more than 3,500 other
candidates that have not yet beenfollowed up.

MOST
DISTANT KNOWN GALAXY DISCOVEREDUniversity of California

Astronomers
have discovered the most distant galaxy yet found. Thegalaxy is seen as it
was 'just' 700 million years after the Big Bang,when the Universe was only
about 5 per cent of its current age of 13.8billion years. The team
identified a very distant galaxy candidate inoptical and infrared images
taken by the Hubble telescope. Follow-upobservations, made in Hawaii by the
Keck telescope with its newmulti-object spectrograph 'MOSFIRE', allowed its
redshift to bedetermined at 7.5 -- the Lyman-alpha emission line of
hydrogen, whosewavelength 'at rest' is far down in the ultraviolet, was
observedshifted into the red part of the spectrum. The observations
showedthat the distant galaxy, prosaically named z8-GND-5296, is
formingstars extremely rapidly -- producing each year stars totalling
about300 times the mass of our Sun, about 100 times the rate of
starformation in the Milky Way.

COULD
A MILKY WAY SUPERNOVA BE VISIBLE IN NEXT 50 YEARS?Ohio State University

Astronomers
have estimated the odds that, some time during the next 50years, a supernova
occurring in our home galaxy will be visible to us.They think it very likely
that such a supernova will be visible totelescopes operating in the
infrared, but the chance that thespectacle would be visible to the naked eye
in the nighttime sky isonly 20 per cent or less. We see supernovae go off
in other galaxiesevery few days, but we could learn more about them if we
can catch onein our Galaxy and study it with all available instruments,
includingnew types such as detectors of neutrinos and gravitational
waves.Astronomers' contingency plans hope to take advantage of the fact
thatsupernovae issue neutrinos immediately after the explosion starts,
butdon't brighten in infrared or visible light until minutes, hours,
oreven days later. So, with luck, neutrino detectors such as
Super-Kamiokande in Japan would sound the alert the moment they
detectneutrinos, and indicate the direction the particles were coming
from.Then infrared detectors could target the location almost
immediately,catching the supernova before the brightening begins.
Gravitational-wave observatories might do the same. Not all neutrinos,
however,come from supernovae -- some come from nuclear reactors, the
Earth'satmosphere or the Sun -- but there have been suggestions as to
howones of supernova origin might be distinguished.

For
those of us who might hope to see a Milky Way supernova with ourown eyes,
however, the chances are low and depend on our latitude --the southern
hemisphere is favoured because most of the Galaxy is seenfrom there. The
last time it happened was in 1604, when JohannesKepler observed one some
20,000 light years away in the constellationOphiuchus. So it would have
been unproductive for anyone to have saton the edge of his chair for the
last 400 years hoping to see the nextone!

INDIA'S
MARS-ORBITER MISSIONThe Planetary Society

The
Indian Space Research Organization has told how its 'PolarSatellite Launch
Vehicle' has placed its Mars-bound spacecraft into ahighly elliptical
parking orbit with a perigee of 248 km and an apogeeof 23,000 km. Over an
interval of about a month, six orbitalmanoeuvres will gradually increase the
distance of the apogee, andfinally a seventh one will put the craft on a
path that will take itto Mars. The cruise to Mars will take about ten
months. Its orbitround Mars will likewise be highly elliptical. The
spacecraftcarries a small payload of five instruments with a total mass of
15kilograms. The scientific goals of the mission have not been speltout
in any detail: "Exploration of Mars surface features, morphology,mineralogy,
and Martian atmosphere by indigenous scientificinstruments." ["Indigenous"
means 'developed in India'.] Theinstruments consist of a Lyman-alpha
photometer, methane sensor,'Exospheric Neutral Composition Analyser', colour
camera andthermal-infrared imaging spectrometer.

But
what this mission is really about is the development of India'scapability in
space -- the technological objectives are the maindrivers. ISRO states
three objectives:1. Design and realisation of a Mars orbiter able
tosurvive and perform Earth-bound manoeuvres, cruise phase of 300
days,Mars orbit insertion/capture, and on-orbit phase around Mars.2.
Deep-space communication, navigation, mission planning andmanagement.3.
Incorporate autonomous features to handle contingency situations.

Each
of the three is a substantial challenge, and achieving any oneof them will
demonstrate new capability for India.

BBC
CONFIRMS THAT 'THE SKY AT NIGHT' WILL CONTINUE

The
BBC has announced that the programme 'The Sky At Night' willcontinue next
year. From February, it will be in a new monthlyhalf-hour slot on BBC4,
with repeats on BBC2. Kim Shillinglaw, Headof Commissioning for BBC Science
and Natural History, says: "SirPatrick Moore inspired generations of
astronomers and I hope that,alongside the BBC's other astronomy content such
as BBC2's StargazingLive, The Sky at Night will enthuse further generations
about thewonder of the night sky." The Sky at Night was first broadcast
on1957 April 24 and continued to be presented by Sir Patrick Moore
untilhis death in 2012, making it the longest-running programme with
thesame presenter in television history. Since Moore's death, theseries
has been fronted by various stand-in presenters.

Bulletin
compiled by Clive Down

(c)
2013 the Society for Popular Astronomy

The
Society for Popular Astronomy has been helping beginners inamateur astronomy
-- and more experienced observers -- for 60 years.If you are not a member
then you may be missing something. Membershiprates are extremely
reasonable, starting at just £18 a year in the UK.You will receive our
bright bi-monthly magazine Popular Astronomy,help and advice in pursuing
your hobby, the chance to hear topastronomers at our regular meetings, and
other benefits. You can joinonline right now with a credit card or debit
card at our livelywebsite: www.popastro.com

Monday, 25 June 2012

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The SOCIETY for POPULAR ASTRONOMY
***********************************
====================================================
Electronic News Bulletin No. 333 2012 June 24
====================================================
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
at our secure site and can take credit and debit cards. You can join
or renew via a secure server or just see how much we have to offer by
visiting http://www.popastro.com/
PLANETS
By Alan Clitherow, Planetary Section Director
We are now entering a rather quiet time for planetary observation
from the UK. Mercury continues to be poorly placed. It is at its
greatest elongation from the Sun, some 26°, at the start of July, but
is very low in the sky when viewed from northern latitudes. On July 1
it will set in the North-West around 1 hour and 25 minutes after the
Sun, but at sunset it will still be only some 10° above the horizon
when viewed from the middle of the UK.
Venus, after its long-anticipated transit across the face of the Sun
on June 6, has become a brilliant morning object. By the start of
July it rises a little more than 2 hours before the Sun and is very
bright at around magnitude -4.3, almost as bright as it gets. At the
moment the illuminated phase is a thin crescent, so observation for
light-diffraction effects in the planet's atmosphere is possible if
you are viewing from far enough south; unfortunately Venus remains
very low in the sky from mid-UK latitudes, making observation
difficult. At sunrise on July 1 Venus is less than 13° above the
eastern horizon.
Mars is still visible, low in the western sky at sunset and setting
around midnight; it is, however, very distant from us at the moment
and presents a tiny disc around 7 arc-seconds in apparent diameter.
Around 89% of the disc is illuminated by the Sun in June and July,
giving an obvious 'phase' with the morning terminator on view, but
the planet's low elevation and tiny size make detailed observation
very difficult.
Perhaps the biggest planetary news at the moment concerns Jupiter.
Jupiter, too, is currently very hard to observe from the UK. It has
passed behind the Sun, from our point of view, and is now a difficult
morning object. From around the Midlands area Jupiter rises at 01.40
UT on July 1, some 2 hours and 10 minutes before the Sun, but it is
only around 17° above the horizon at sunrise. The air can be
surprisingly steady at that time, so it is worth at least attempting
to view Jupiter to find out what is going on at the North Equatorial
Belt (NEB). As reported in May, when Jupiter moved too close to the
Sun for effective observation, there were suggestions that there was
about to be a major outbreak in the NEB. In recent years that dark
turbulent belt of cloud has followed a cycle of narrowing and
expanding, and in April was particularly narrow -- certainly as thin
as I have ever seen it. In addition, certain details in the belt were
unusual. The dark stretched patches that often float on the edges of
the belt (called Barges because of their shape) were left completely
isolated from it, as though 'beached' if I can stretch the analogy
that far. Also the cloud patterns in the belt and dark projections
that push out from the belt into the surrounding light zones were
unusually small and faster-moving than normal. Recent observations,
made in Greece and reported to the British Astronomical Association,
suggest that a number of dark spots and at least one larger white spot
have appeared on the NEB along with colour changes in the surrounding
zones. The last major expansion of the NEB occurred in 2009 and was
preceded by just such activity. As the year moves on, Jupiter will
become easier to observe, and I recommend that we pay close attention
to those features to see how they develop.
Saturn is still an early-evening object and remains so through the
rest of June and into July. The light summer evenings and the planet's
low elevation make high-resolution imaging or detailed observation
increasingly difficult. It will remain visible as a low evening
object well into the autumn. Observation of the outer planets, Uranus
and Neptune, is best left until the autumn when they will be better
placed in a properly dark sky.
Thank you and, as usual, please submit any observing reports you may
have via the planetary-section website.
JUPITER'S FAINTEST KNOWN MOON
Phys.org
In 2010 September, two previously unknown distant satellites of
Jupiter were discovered during routine tracking observations of
already-known moons. They were re-observed several times during that
autumn, in order to see if they really were satellites of Jupiter,
leading to their obtaining MPC designations S/2010 J 1 and S/2010 J 2.
With Jupiter now having 67 known satellites, the discovery of two
additional tiny satellites does not have a large bearing on our
understanding of the system. S/2010 J 1 was discovered in images
taken at the Palomar 200-inch Hale Telescope and S/2010 J 2 was
discovered in ones taken with the MegaCam mosaic CCD camera at the
3.6-m CFHT. Upon later inspection, S/2010 J 2 was also weakly visible
in the images from Palomar. Observations in 2010 October and November
and 2011 January allowed the orbits to be determined well enough to
confirm that they are indeed satellites and not just nearby asteroids,
allowing IAU designations to be granted in 2011 June. Further follow-
up observations have refined the orbits sufficiently for the
satellites' positions to be reliably be predicted several years into
the future.
During 2003 the CFHT observed the entire region around Jupiter in a
search for moons. Several faint objects were detected that were never
classified as satellites because they were not recovered in follow-up
observations. However, with well determined orbits of S/2010 J 1 and
2, it was possible to extrapolate backwards in time to 2003, and J 1
was indeed found in several images, although J 2 could not be located
in any of them. That is, however, not surprising, as J 2 is the
faintest Jupiter satellite observed to date, and ideal conditions are
required to see it, even with the CFHT. On the basis of their
brightnesses, the diameters of the moons can be estimated at about
3 km for J 1 and 2 km for J 2 . It is believed that nearly all moons
the size of J 1 or larger have been discovered, but there must be
dozens of undiscovered satellites in the 1-3-km class. J 1 is in an
orbit with an average distance (semi-major axis) from Jupiter of 23.45
million km and orbital period of 2.02 years, while J 2 has a
semi-major axis of 21.01 million km and an orbital period of 1.69
years. The irregular satellites of the giant planets are clustered in
'families' with similar orbits and colours. The families are believed
to have formed as a result of collisions of passing comets or
asteroids with former larger moons long ago. J 1 appears to belong to
the Carme group, and J 2 appears to belong to the Ananke group.
FEW BROWN DWARFS CLOSE TO HOME
NASA/Jet Propulsion Laboratory
The Wide-field Infrared Survey Explorer (WISE) was launched in 2009
and surveyed the entire sky in infrared light in 2010. One of the
mission's main scientific goals was to survey the sky for brown
dwarfs. Those small bodies start their lives like stars, but lack the
mass required to burn nuclear fuel. With time, they cool and fade,
making them difficult to find. WISE has better sensitivity than
previous infrared missions and has been able to pick up many brown
dwarfs, but there seem to be far fewer of them than some 'experts' had
predicted. In 2011 August, the mission announced the discovery of the
coolest brown dwarfs observed yet, a new class of stars called Y
dwarfs. One of the Y dwarfs has a temperature below 25°C, about room
temperature, making it the coldest star-like body known. Since then,
the WISE team has found 200 brown dwarfs, including 13 Y dwarfs.
Determining the distances to the objects is a key factor in estimating
their population density in our neighbourhood. After measuring the
distances to several of the coldest ones, the scientists fell back on
estimates of the distances to all the others. They concluded that
there are about 33 brown dwarfs within 8 parsecs of Sun. There are
211 stars known within that distance -- about six stars to every brown
dwarf. The results are still preliminary: it is likely that WISE will
discover additional Y dwarfs, but not in vast numbers.
SMALL PLANETS CAN FORM EVEN AROUND METAL-DEFICIENT STARS
NASA
The formation of planets has been thought to occur mostly around stars
rich in heavy elements such as iron and silicon. Astronomers refer to
all chemical elements heavier than hydrogen and helium as metals.
They define metallicity as the metal content of a star. Stars with a
higher fraction of heavy elements than the Sun are considered
metal-rich.
Planets are created in discs of gas and dust around new stars. The
metallicity of a disc mirrors the metallicity of the star. Planets
like the Earth are composed almost entirely of elements such as iron,
oxygen, silicon and magnesium. Astronomers have hypothesized that
large quantities of heavy elements in the disc would lead to more
efficient planet formation. It has been noted that giant planets with
short orbital periods tend to be associated with metal-rich stars, but
new ground-based observations, combined with data collected by the
Kepler space telescope, show that small planets form around stars with
a wide range of heavy-element content. An international research team
studied the elemental composition of more than 150 stars having 226
planet candidates smaller than Neptune, and found that small planets
form around stars with a wide range of heavy-metal content, including
stars with only 25% of the Sun's metallicity.
BLACK HOLES 'CHANGE GEAR'
RAS
Black holes are extremely powerful and efficient engines that not only
swallow matter, but also return a lot of energy to the Universe in
exchange for the mass they consume. When black holes attract mass
they also trigger the release of intense X-ray radiation and power
strong jets. Black-hole jets -- lighthouse-like beams of material
ejected at close to the speed of light -- can have a major impact on
the evolution of their environment. For example, jets from the
super-massive black holes found at the centres of galaxies can blow
huge bubbles in clusters of galaxies, and heat the gas in them.
Another example of what black-hole jets can do is known as Hanny's
Voorwerp, a cloud of gas where stars started forming after it was hit
by the jet of a black hole in a neighbouring galaxy. Those phenomena
aroused interest in the way black holes produce and distribute energy.
In 2003 it became clear that there is a relationship between the X-ray
emission from a black hole and its jet outflow, which needs to be
explained if we want to understand how the black-hole engine works.
At first it seemed that the relationship was the same for all feeding
black holes, but counter-examples were soon found. They still showed
a connection between the energy released in the X-ray emission and
that put in the jet ejection, but the proportion differed from that in
the 'standard' black holes. As the number of such examples grew, it
started to appear that there were two groups of black-hole engines
working in slightly different ways.
Recently a team of astronomers found a black hole that seemed to
switch between the two regimes of X-ray/jet proportion, depending on
how its brightness changed. That suggested that black holes do not
necessarily come with two different engines, but that each black hole
can run in two different regimes. Then two more examples were found
of black holes that could 'change gear', suggesting that changing gear
might be a common property of black holes. The switch happens at a
similar X-ray luminosity for all three of the black holes. Those
discoveries provide new input to theoretical models that hope to
explain both the functioning of the black-hole engine itself and its
impact on the surrounding environment.
FIRST OBJECTS BURNED FURIOUSLY
ScienceDaily
The faint, lumpy glow given off by the very first objects in the
Universe may have been detected, with the best precision yet, by the
Spitzer space telescope. Those faint objects might be very massive
stars or voracious black holes. They are too far away to be seen
individually, but Spitzer has captured rather convincing evidence of
what appears to be the collective pattern of their infrared light.
The observations help to confirm that the first objects were numerous
in quantity and furiously burned cosmic fuel, and would have been
tremendously bright. Astronomers cannot yet directly rule out other,
more mundane, sources for that light, but it is becoming increasingly
likely that they are catching a glimpse of an ancient epoch.
Spitzer first caught hints of that remote pattern of light, known as
the cosmic infrared background, in 2005, and again with more precision
in 2007. Now, Spitzer is in the extended phase of its mission, during
which it performs more in-depth studies on specific patches of the
sky. Astronomers used Spitzer to look at two patches of sky for more
than 400 hours each. The team then carefully subtracted all the known
stars and galaxies in the images. Rather than being left with a
black, empty patch of sky, they found faint patterns of light with
several telltale characteristics of the cosmic infrared background.
The lumps in the observed pattern are consistent with the way the very
distant objects are thought to be clustered together. The Universe
formed 13.7 billion years ago in an, explosive Big Bang. With time,
it cooled, and after about 500 million years the first stars, galaxies
and black holes began to take shape. Astronomers say that Spitzer may
be seeing some of that 'first light'. It would have originated at
visible or even ultraviolet wavelengths and then, because of the
expansion of the Universe, stretched out to the longer, infrared
wavelengths observed by Spitzer. The new study improves on previous
observations by measuring that cosmic infrared background at angular
scales of up to 1° -- significantly larger than before.
PLAN APPROVED FOR BIGGEST TELESCOPE
ESO
ESO is to build the largest optical/infrared telescope in the world.
At its meeting in Garching earlier this month, the ESO Council
approved the European Extremely Large Telescope (E-ELT), subject to
confirmation by the authorities in four of the member countries. The
E-ELT will be a 39.3-m segmented-mirror telescope sited on Cerro
Armazones in northern Chile, close to the Paranal Observatory, and
will start operations early in the next decade. Spending on elements
of the project other than the initial civil works will not commence,
however, until the contributions pledged by the member states, as
agreed in funding principles approved by the Council in late 2011,
exceed 90% of the 1083-million-euro cost (at 2012 prices). Early
contracts for the project have already been placed. Shortly before
the Council meeting, a contract was signed to begin a detailed design
study for the very challenging adaptive mirror of the telescope. That
has one of the longest lead-times in the E-ELT programme, and an early
start was essential. Civil works that are expected to begin this year
include preparation of the access road to the summit of Cerro
Armazones and the levelling of the summit itself.
The year 2012 marks the 50th anniversary of the founding of the
European Southern Observatory. ESO is supported by 15 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France,
Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden,
Switzerland and the United Kingdom. It operates on three sites in
Chile -- La Silla, Paranal and (in partnership) Chajnantor.
Bulletin compiled by Clive Down
(c) 2012 the Society for Popular Astronomy
The Society for Popular Astronomy has been helping beginners to
amateur astronomy -- and more experienced observers -- for nearly 60
years. If you are not a member then you may be missing something.
Membership rates are extremely reasonable, starting at just £18 a
year in the UK. You will receive our bright bi-monthly magazine
Popular Astronomy, help and advice in pursuing your hobby, the chance
to hear top astronomers at our regular meetings, and other benefits.
The best news is that you can join online right now with a credit
card or debit card at our lively website: www.popastro.com
====================================================================

Tuesday, 15 May 2012

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The SOCIETY for POPULAR ASTRONOMY
***********************************
====================================================
Electronic News Bulletin No. 287 2010 April 25
====================================================
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
at our secure site and can take credit and debit cards. You can join
or renew via a secure server or just see how much we have to offer by
visiting http://www.popastro.com/
EARLY APRIL FIREBALLS
By Alastair McBeath, SPA Meteor Section Director
The first part of April this year has brought a healthy crop of fireballs
(meteors of magnitude -3 or brighter) to the Section so far. Single-
observer meteors were reported at 03:17 UT on April 6-7 (magnitude
-7, seen from Edinburgh), about 04:25 UT on April 11-12 (very bright;
Cornwall) and 21:31 UT on April 14-15 (-5/-7; Gwent), plus there
were two others seen from more than one location.
At 20:15 ± 5 minutes UT on April 9-10, a magnitude -10 or so
meteor was spotted from Glasgow and Edinburgh. Reports from the
witnesses suggested the object may have followed a roughly south to
north trajectory over eastern Scotland north of the Fife peninsula,
perhaps across part of the eastern Grampian Mountains of the
"Aberdeen angle", or the North Sea offshore of there.
On April 16-17 near 22:00 UT, a very bright, green fireball was seen
from four locations in southern England - Gloucester, Surrey, Hampshire,
and Devon. Two of the initial sightings can be found on the UK Weather
World's Space Weather Forum (at: http://snipurl.com/vobdi ). This
fireball seemed to have been out high above the western Channel, and
part of its flight may have been some way offshore of the English coast
between roughly Prawle Point in Devon and Lizard Point in Cornwall.
Most observers were impressed both by its brilliance and its vivid green
colour, though suggestions the colour may have been due to the volcanic
ash cloud over and near the British Isles from Iceland, were without
foundation. Bright green, though not common, does occur in meteors,
particularly the brighter ones, without any such assistance.
All further sightings of these, or other fireballs, made from the British
Isles and nearby, would be welcomed by the Section. The minimum
details required are:
1) Exactly where you were (give the name of the nearest town or large
village and county if in Britain, or your geographic latitude and longitude
if elsewhere in the world);
2) The date and timing of the event in UT (remember to subtract one
hour from current clock time, BST, to get UT); and
3) Where the fireball started and ended in the sky, as accurately as
possible, or where the first and last points you could see of the trail were
if you did not see the whole flight.
More advice and a fuller set of details to send (including an e-mail
report form) are given on the "Making and Reporting Fireball
Observations" page of the SPA website, at: http://snipurl.com/u8aer .
The Easter break has also prompted another flurry of "sky lantern"
sightings, sadly. These were last so problematic back in January (see
ENB 280, at: http://snipurl.com/ucps9 ). In order not to miss genuine
fireball observations, the Meteor Section is willing to receive reports of
any unusual moving star-like light in the sky, where the witness could not
be sure what the object was. However, it is very important to send as
many details as possible - ideally completing the electronic Fireball
Report Form fully - to enable the object's nature to be determined
swiftly and accurately. An unhelpfully large number of the recent
potential lantern sightings have had insufficient information provided
initially to allow this, to the extent some could even have been genuine
fireballs. Please remember this when sending in a possible fireball
sighting, and help us to better help you!
BRILLIANT IMAGED FIREBALL OVER THE USA
By Alastair McBeath, SPA Meteor Section Director
Around 22:05 local time on April 14, a spectacular fireball was seen
from at least six states in the Midwest and Great Lakes regions of the
USA, lighting-up the sky. Video recordings of the very slow, brilliant
meteor were made by-chance, which were quickly picked-up by TV
news stations and broadcast across the world. The videos are available
online - try the BBC's News webpage at http://snipurl.com/voeg5 , for
instance - while there are more comments, and links to additional
Internet sites on the UK Weather World's Space Weather Forum topic
at: http://snipurl.com/voekk .
As too often, an immediate claim was made that the fireball had come
from a meteor shower, this time the very minor Gamma Virginids, based
on nothing more than a wild guess, because of when it had happened.
Another week, and doubtless it would have been called a Lyrid! If the
videos as broadcast were accurate to the object's appearance, especially
its apparent speed, the actual fireball seemed to have been well below
the slow-medium atmospheric velocity, around 30 km/sec, expected for
the Virginids or any of the Antihelion Source meteors (as we currently
term meteors from the many, very weak, radiants clustered near the
ecliptic nearly opposite the Sun in the sky, and active for most of the
year - see the April meteor activity webpage for notes on the Antihelion
Source this month, at http://snipurl.com/vogzo ). None of this detracts
from the magnificence of the fireball, of course!
COMET McNAUGHT HAD UNUSUALLY LONG ION TAIL
RAS
British scientists have shown from Ulysses spacecraft data that Comet
McNaught, which in early 2007 became the brightest comet seen for 40
years, disturbed a region of space much larger than that occupied by
the visible tail. Analysis of magnetometer data suggests that the
comet was surrounded by a shock wave created where the fast-flowing
particles of the solar wind were slowed down abruptly when they
impinged on the ionized gas emitted from the comet's nucleus. It was
just by chance that Ulysses happened to pass through Comet McNaught's
tail; it encountered the tail of ionized gas at a distance downstream
of the comet's nucleus more than 1.5 times the distance between the
Earth and the Sun -- much further away than the visible dust tail
extended. Ulysses took 8 days to traverse the shocked solar wind
surrounding Comet McNaught, compared to 2.5 days in shocked wind
surrounding Comet Hyakutake in 1996. The Giotto spacecraft's
encounter with Comet Grigg-Skjellerup in 1992 took less than an hour
from one shock crossing to another; to cross the shocked region at
Comet Halley took a few hours. The comparisons show that Comet
McNaught was not only spectacular from the ground but was an unusually
large obstacle to the solar wind.
VENUS IS VOLCANICALLY ACTIVE
ESA
Venus Express has returned the clearest indication yet that Venus is
still active. Relatively young lava flows have been identified by
their emission of infrared radiation. The finding suggests that the
planet remains capable of volcanic eruptions. The sparseness of
craters on Venus suggests that something is wiping the planet's surface
clean. That something is thought to be volcanic activity, but the
question is whether it happens quickly or slowly -- whether there is
some sort of cataclysmic volcanic activity that resurfaces the entire
planet with lava, or a gradual sequence of smaller volcanic eruptions.
The latter are suggested by maps of the infrared brightness or
'emissivity'. Astronomers concentrated on three regions that are
analogous to Hawaii, well-known for its active vulcanism. Those
regions on Venus have higher emissivities than their surroundings,
indicating different compositions. On Earth, lava flows react rapidly
with oxygen and other elements in the atmosphere, changing their
composition. On Venus, the process should be similar, though more
vigorous because of the hotter, denser atmosphere. The researchers
interpret the areas of high emissivity as lava flows that have not
undergone as much weathering as their surroundings, implying that they
are relatively recent, possibly even still forming.
PLUTO SHOWS CHANGES
NASA
A comparison of Hubble Telescope images of Pluto obtained in 1994 and
2003 shows that the northern hemisphere has brightened while the
southern hemisphere has dimmed. Ground-based observations suggest
that Pluto's atmosphere doubled in mass during approximately the same
interval. Pluto gets so cold that its atmosphere can actually freeze
and fall to the ground. If the Earth's atmosphere did that, it would
make a layer 30 feet thick, but Pluto has far less atmosphere. When
it is on the ground, Pluto's entire blanket of air is no more than
a frosty film of nitrogen and methane. Until the mid-1980s, Pluto's
northern hemisphere had been tilted away from the Sun for over 100
years, accumulating a substantial amount of frost. Now the northern
hemisphere is coming into sunlight and appears, as shown in the Hubble
images, to have been growing brighter. The atmosphere might also be
changing in response to Pluto's highly eccentric orbit. During the
late 1980s, Pluto approached as close to the Sun as it ever gets and
was consequently warming. Surface frosts exposed to such 'warmth' may
be subliming -- that is, changing back into gas.
DUSTY DISCS IN PLANETARY SYSTEMS
RAS
Two stars observed in the infrared with the MIDI interferometer, which
combines the light from the 8-m units of the VLT in Chile, appear to
have discs of rocky and dusty material at distances comparable to that
from the Earth to the Sun. The stars concerned, both considerably
younger than the Sun, are HD 69830, of spectral type K0 V, in the
constellation Puppis and thought to have three planets with masses
comparable to Neptune, and Eta Corvi, type F2 V. Earlier observations
had indicated that both stars had discs; Eta Corvi is known to have
cold material around it at a distance of 150 Astronomical Units
(Earth--Sun distances; 1 AU is about 150 million km). With MIDI a
relatively small dusty disc around HD 69830 was clearly seen; it lies
between 7.5 and 360 million km from the star. A similar disc was
found close to Eta Corvi, lying between 24 to 450 million km out.
Those results represent the first resolution of dusty discs so close
to their parent stars.
COOLEST BROWN DWARF FOUND NEAR SUN
University of Hertfordshire
Brown dwarfs are bodies with masses in the range between those of
giant planets and the faintest stars. Some are isolated, while others
orbit normal stars or exist in star clusters. Astronomers have now
discovered a previously unknown brown dwarf just 2.9 parsecs (9 light-
years) away -- the seventh-closest star, and the first to be found
so close since Luyten 726-8 was discovered in 1948. The star, UGPS
J0722-05, has a temperature of 400-500 K and is far less luminous and
significantly cooler than previously known objects. The Jupiter-sized
object emits only 0.000026% as much energy as the Sun. Since 1995,
more than 100 methane brown dwarfs, or T dwarfs, have been found, with
spectra similar to that of the planet Jupiter and with effective
temperatures in the range 500-1300 K. The detection of even cooler
bodies will open a new arena for atmospheric physics and may help to
determine the formation rate of stars and brown dwarfs in our Galaxy
as a function of both mass and time.
ROCKY PLANETS MAY BE COMMON IN THE MILKY WAY
RAS
Astronomers have found evidence that rocky planets are commonplace in
our Galaxy. A survey of white dwarfs, the compact remnants of stars
that were once like our Sun, found that many show signs of
contamination by heavier elements and possibly water. White dwarfs
are the endpoint of stellar evolution for the vast majority (>90%) of
all stars in the Milky Way. Because they ought to have almost pure
hydrogen or helium atmospheres, if heavier elements such as calcium,
magnesium and iron are found then they are interpreted as external
pollutants. For decades, it was believed that the interstellar
medium (the tenuous gas between the stars) was the source of the
metals in the polluted white dwarfs. The team used data from the Sloan
Digital Sky Survey (SDSS), a project that aims to survey the sky in
infrared light, imaging more than 100 million objects and following up
1 million of them by obtaining their spectra. By examining the
positions, motions and spectra of the white dwarfs identified in the
SDSS, the team shows that an interstellar origin for the metals is no
longer a satisfactory theory. Instead, rocky planetary debris is
probably the usual culprit. The new work indicates that at least 3%
and perhaps as much as 20% of all white dwarfs are contaminated in
this way, with the debris most likely in the form of rocky minor
planets with a total mass of about that of an asteroid 140 km in
diameter. That implies that a similar proportion of stars like our
Sun, as well as stars that are somewhat more massive, like Vega and
Fomalhaut, build terrestrial-type planetary systems. The scientists
also measured the composition of the pollutants through their
spectroscopic signatures, which stand out in the otherwise pure
atmosphere of the white dwarfs. It appears that a significant
fraction of the stars are polluted with material that contained water,
with implications for the frequency of habitable planets around
other stars.
BLACK HOLES AND GALAXY DEATH
RAS
Black holes are thought to reside at the centre of almost every
galaxy, with some growing to more than a billion times the mass of the
Sun. Now a team of UK astronomers has proposed that such super-
massive black holes are commonplace, release more than enough
energy to strip their host galaxies apart, and in the process shut
down star formation in their galaxies for good. For many years black
holes have fascinated scientists and the public alike, with their
peculiar ability to warp space and time and their sinister tendency to
devour everything they encounter. Before matter falls in, as it
swirls around the black hole it forms an 'accretion disc', where it
heats up and radiates energy. The super-massive black holes have such
strong gravitational fields that the infalling matter releases a vast
amount of energy, making each accretion disc far brighter than the
combined output of the billions of stars in the galaxy around it.
One of the consequences of such outpouring of energy is that it drives
away cool gas and dust, the raw ingredients of new stars. That
permanently shuts down star-formation in the surrounding galaxy, whose
remaining stars age, end their lives, and are never replaced. The new
study considered the role of super-massive black holes in the
development of galaxies. To search for them, the team used the Hubble
telescope and the Chandra X-ray observatory to observe in optical,
near-infrared and X-ray light. In particular, the astronomers looked
for galaxies which have a very high emission of X-rays, a probable
signature of black holes devouring gas and dust. From the space
telescopes' data astronomers find that at least 1/3 of all the massive
galaxies they observed not only contain super-massive black holes,
but that at some point in their histories the emission from the holes'
accretion discs far outshines the galaxies themselves. The energy
output of regions around the black holes is high enough to strip apart
every massive galaxy in the cosmos 25 times over, whilst the X-ray
emission from them turns out to dwarf that from every other source in
the Universe put together.
POSSIBLE MICROQUASAR IN STARBURST GALAXY M82
RAS
Radio astronomers at Jodrell Bank have discovered a strange new object
in M82, a galaxy that is 10 million light-years away and is forming
new stars at a prodigious rate, many of them massive stars that die
quickly, a supernova explosion occurring every 20 to 30 years. The
new object, which appeared last May, has perplexed astronomers, who
have never seen anything quite like it before. The object turned on
very rapidly within a few days and has shown no sign of decaying in
brightness over the first months of its existence. The new young
supernova explosions that astronomers expect to see in M82 brighten at
radio wavelengths over several weeks and then decay over several
months, so that explanation seems unlikely. The plausibility of a
supernova explanation was further undermined when very accurate
positional monitoring by the UK network of radio telescopes, MERLIN,
tentatively detected a change in position for the object over the
first 50 days. It was equivalent to an apparent motion of over four
times the speed of light. Such large apparent velocities are not seen
in supernova remnants and are usually only found with relativistic
jets ejected from accretion discs around massive black-hole systems.
The nucleus of M82 may contain a super-massive black hole. The new
detection lies at a position close to, but several arcseconds away
from, the dynamical centre of M82 -- far enough away that it would
seem unlikely that this object is associated with the central
collapsed core of the galaxy. The new source could be the first radio
detection of an extragalactic 'micro-quasar'. Examples of such
systems within the Milky Way are found as X-ray binaries with
relativistic jets ejected from an accretion disc around a collapsed
star fuelled with material dragged from a close binary companion.
However, this object would be brighter than any Galactic example yet
detected, has lasted months longer than any known X-ray binary, and
lies at a position in M82 where no variable X-ray source has been yet
been detected.
LOFAR OPENS UP LOW-FREQUENCY UNIVERSE
RAS
The Low Frequency Array (LOFAR), a new pan-European radio-astronomy
instrument, has started mapping the Universe at very long wavelengths,
a part of the electromagnetic spectrum that is relatively unexplored.
Astronomers hope LOFAR will allow them to study cosmic rays, pulsars,
and the magnetic field within our own and nearby galaxies. LOFAR will
also compile a census of radio-emitting galaxies from the very early
Universe, which may help us to understand how galaxies formed and
evolved over cosmic time.
NEXT BULLETIN
Owing to holidays, the next scheduled bulletin will be issued on May 16.
Bulletin compiled by Clive Down
(c) 2010 the Society for Popular Astronomy
The Society for Popular Astronomy has been helping beginners to
amateur astronomy -- and more experienced observers -- for more than
50 years. If you are not a member then you may be missing something.
Membership rates are extremely reasonable, starting at just £16 a year
in the UK. You will receive our bright quarterly magazine Popular
Astronomy, regular printed News Circulars, help and advice in pursuing
your hobby, the chance to hear top astronomers at our regular
meetings, and other benefits. The best news is that you can join
online right now with a credit card or debit card at our lively
website: http://www.popastro.com/
Astronomica is a firm set up by astronomers to sell astronomical
equipment at affordable prices, and offers SPA members a 10% discount
on all products. Details of any special offers can be found at
http://www.astronomica.co.uk

Sunday, 1 January 2012

***********************************
The SOCIETY for POPULAR ASTRONOMY
***********************************
====================================================
Electronic News Bulletin No. 324 2012 January 1
====================================================
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
at our secure site and can take credit and debit cards. You can join
or renew via a secure server or just see how much we have to offer by
visiting http://www.popastro.com/
COMET LOVEJOY PLUNGES PAST THE SUN AND SURVIVES
NASA
In mid-December there was an exciting event, when Comet Lovejoy passed
through the Sun's corona and emerged intact. The comet's close
encounter was recorded by at least five spacecraft. In movies made by
the SDO (Solar Dynamics Observatory), the comet's tail was seen to
wriggle wildly, no doubt as a result of electrical or magnetic
interaction in the corona, as the comet plunged through the Sun's
corona only 120,000 km above the photosphere. Comet Lovejoy was
discovered on December 2 by amateur astronomer Terry Lovejoy in
Australia. Researchers quickly realized that the new find was a
member of the Kreutz family of Sun-grazing comets. Named after the
German astronomer Heinrich Kreutz, who first studied them, Sun-grazers
are fragments of a giant comet that broke apart in the 12th century
(probably the Great Comet of 1106). Kreutz Sun-grazers are very
numerous and typically small (~10 metres), although there have been
major examples such as Ikeya-Seki in 1965, which on the day of
perihelion passage was visible to the naked eye in full daylight (the
Sun of course having to be hidden from view behind a chimney or
something!) The Solar and Heliospheric Observatory sees one falling
into the Sun every few days. At the time of discovery, Comet Lovejoy
appeared to be much larger than the usual run of Kreutz Sun-grazers,
perhaps in the 100-200-m range, but researchers are revising those
numbers upward.
ASTRONOMERS FIND EARTH-SIZED PLANETS
NASA
Astronomers think that they have found two Earth-sized planets
orbiting a star similar to the Sun. The discovery follows
confirmation last month of a super-Earth-sized planet, called
Kepler-22b, that circles the right distance from its parent star for
liquid water to exist on its surface. The newly discovered planets,
called Kepler-20e and 20f, have at least three gas-giant siblings, in
one of the larger planetary systems found to date. But the family is
nothing like our Solar System, where rocky planets like Venus, the
Earth and Mars are grouped together relatively near the Sun, while gas
giants like Jupiter and Saturn are segregated in the outer regions.
The two Earth-like and three Neptune-sized planets in the Kepler-20
system are interspersed, and all of them orbit closer to the parent
star than Mercury does to the Sun. The system is located about 1,000
light-years away in the constellation Lyra.
RAPID STAR FORMATION IN A GALAXY ALMOST AT THE DAWN OF TIME
University of California
One of the most distant galaxies known, GN-108036, which is at a
red-shift of 7.2 and a distance of about 12.9 billion light-years, has
been found to be forming stars at a particularly high rate. The
galaxy is the brightest one found to date at such a great distance.
An international team of astronomers using the Japanese Subaru
telescope on Mauna Kea in Hawaii first identified it; then infrared
observations from Spitzer and Hubble were used to estimate that the
galaxy's star-formation rate is equivalent to about 100 Suns per year.
For comparison, our Milky Way galaxy is about five times larger and
100 times more massive than GN-108036, but makes stars at a rate of
about 3 Suns per year. The discovery is surprising, because previous
surveys had not found such bright galaxies so early in the history of
the Universe. According to the researchers, GN-108036 may be a
special, rare object that they happened to observe during an extreme
burst of star formation.
Bulletin compiled by Clive Down
(c) 2012 the Society for Popular Astronomy
The Society for Popular Astronomy has been helping beginners to
amateur astronomy -- and more experienced observers -- for more than
50 years. If you are not a member then you may be missing something.
Membership rates are extremely reasonable, starting at just £16 a year
in the UK. You will receive our bright bi-monthly magazine Popular
Astronomy, help and advice in pursuing your hobby, the chance to hear
top astronomers at our regular meetings, and other benefits. The best
news is that you can join online right now with a credit card or debit
card at our lively website: http://www.popastro.com/

Sunday, 6 November 2011

***********************************
The SOCIETY for POPULAR ASTRONOMY
***********************************
====================================================
Electronic News Bulletin No. 320 2011 November 6
====================================================
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is one of Britain's liveliest astronomical
societies, with members all over the world. We accept subscription
payments online at our secure site and can take credit and debit
cards. You can join or renew via a secure server or just see how much
we have to offer by visiting http://www.popastro.com/
SOLAR ACTIVITY
By Richard Bailey, SPA Solar Section Director
One of the largest active regions in years, AR 1339, has come into
view around the east limb of the Sun, and will change shape over the
coming days. It could be a source of flares, as well as filaments and
bright plaging. The main sunspot is Earth-sized. It can be viewed by
projecting an image of it with a telescope or binoculars onto a shaded
white screen, of with specialist solar-filter systems. To see any
flares, filaments and plaging, H-alpha filter systems will be needed.
A picture of the sunspot can be seen on the Solar link from the SPA
website, under News. No attempt must be made to see it by looking
directly at the Sun, as permanent eye damage could result.
COMET SECTION NEWS
By Jonathan Shanklin, Comet Section Director
The remains of comet 2010 X1 (Elenin) have been recovered after
perihelion by a Spanish observer, working at a remote mountain
location in the Cantabrian Mountains. The comet was probably a small
object as it had a faint absolute magnitude, and as it approached
perihelion it was seen to become more diffuse and fade. In October,
over a month after perihelion, Juan Gonzalez detected a cloud of
material in the expected location, though his observations were
doubted by many Internet 'experts'. They believed that it had
completely disintegrated, and when no object could be detected by deep
imaging, they poured scorn on the visual observation. They should
have remembered history. Similar scorn was heaped on George Alcock
when he drew intricate tail detail, but newer technology showed that
his visual observations were correct. The long-exposure photographs
of the mid-twentieth century had simply blurred out the structure. In
the case of the recent disputed observation, amateur wide-field CCD
imaging was able (after a few days) to provide the proof that the
visual observation was correct. A superb image taken remotely by
Rolando Ligustri showed a diffuse cloud of material representing the
disintegrated comet. The lesson is that visual observation still has
a part to play in scientific discovery.
There is a comet that is well placed for observation if you want to
see what one looks like. From light-polluted city skies comet 2009 P1
(Garradd) is not easy in binoculars, but in darker rural skies you get
a more impressive view. Observations so far show it to have a small,
moderately condensed coma about 4 or 5 minutes of arc in diameter, but
from my urban location I have not been able to see anything of a tail.
Its brightness has not changed much over the last month, as its
decreasing distance from the Sun is balanced by its increasing
distance from us. The comet will reach perihelion at 1.6 AU just
before Christmas, but it is then 2 AU from the Earth. It should be
around 7th magnitude, much as it is at the moment. In the new year it
will be receding from the Sun, but our distance from it is decreasing,
and the comet could become a little brighter. The comet is nearly
stationary in southern Hercules in November, but then accelerates
northwards, though it is still in Hercules at the end of the year.
http://www.ast.cam.ac.uk/~jds/
PLANETS
By Andrew Robertson, SPA Planetary Section Director
MERCURY reaches eastern elongation on the 14th (23°) but being at only
4° altitude at sunset is effectively unobservable from the UK.
VENUS is only slightly better placed, being at 6° altitude at sunset
on the 14th, but as it is magnitude -3.9 (compared to Mercury's -0.2)
there is a good chance of locating it towards the end of the month
just after sunset in the SSW when it will be 8° altitude, provided
you have a clear sky and horizon.
MARS is an early-morning object. By mid-month at the end of
astronomical dark (0515 UT) it is at 47° altitude in the SSE shining
at magnitude 1.0 in Leo, near to Regulus which being a blue-white star
of magnitude 1.4 will make a pleasant pairing.
JUPITER is still king of the planets, having just passed opposition on
October 29 and shining at magnitude -2.8. It is observable most of
the night. Displaying a diameter of 49" it shows a wealth of detail
even in a small telescope, and I have been receiving lots of images
and sketches from SPA members.
Any reports of observations would be most welcome via:
http://popastro.com/planet/contact/
You can see a selection of members' images/sketches at:
http://snipurl.com/12a79y
ASTEROID 2005 YU55 TO APPROACH THE EARTH ON 2011 NOVEMBER 8
NASA
Near-Earth asteroid 2005 YU55 will pass within 0.85 lunar distances
of the Earth on November 8. The close approach of this 400-metre
C-type asteroid presents an excellent opportunity for optical, near-
infrared and radar observations. On November 8 and 9 the object will
reach visual magnitude 11 and should be easily visible in modest
telescopes. The closest approach to the Earth and the Moon will be
respectively 0.00217 AU and 0.00160 AU on November 8 at 23:28 and
November 9 at 07:13 UT. Discovered on 2005 December 28 by the
Spacewatch Program, the object has been previously observed with the
Arecibo radar in 2010 and shown to be a very dark, nearly spherical
object 400 metres in diameter. As well as aiding the interpretation
of the radar observations, visual and near-infrared observations could
define the object's rotational characteristics and provide constraints
on the nature of the object's surface roughness and mineral
composition. Since the asteroid will approach the Earth from the
Sunward direction, it will be a daylight object until the time of
closest approach. Although classified as a potentially hazardous
object, 2005 YU55 poses no threat of an Earth collision over at least
the next 100 years. However, this will be the closest approach to
date by an object of such a large size that we know about in advance,
and (as far as is known) such an event will not happen again until
2028 when asteroid (153814) 2001 WN5 will pass to within 0.6 lunar
distances.
ERIS IS PLUTO'S TWIN
ESO
Eris is one of the largest trans-Neptunian 'Kuiper-Belt' objects in
the outer Solar System; it was discovered in 2005, and its discovery
was one of the factors that led to the adoption by the IAU of a new
class of objects called dwarf planets and the re-classification of
Pluto from planet to dwarf planet in 2006. Eris is currently three
times further from the Sun than Pluto. In 2010 November, it occulted
a faint background star; such occurrences are rare and difficult to
observe, as Eris is so distant and its angular diameter is so small.
Occultations provide the most accurate, and often the only, way to
measure the shape and size of a distant Solar-System body.
Observations were attempted from 26 locations around the globe,
including several telescopes at amateur observatories, on the
predicted path of the shadow, but only at two sites, both in Chile, at
one of which there were two telescopes, was an actual occultation
observed. The combined observations from the two Chilean sites are
consonant with a model of Eris that is close to spherical.
While earlier observations by other methods suggested that Eris was
probably about 25% larger than Pluto, with an estimated diameter of
3000 km, the new study indicates that the two objects are pretty well
the same size. Eris's newly determined diameter stands at 2326 km,
with an accuracy assessed at 12 km -- but that is valid only on the
assumption that the object is a sphere. Pluto has a diameter
estimated to be between 2300 and 2400 km. Pluto's diameter is harder
to measure because of the presence of an atmosphere, albeit very
tenuous, which creates ambiguities in the understanding of occultation
light-curves.
The motion of Eris's satellite Dysnomia enables the mass of Eris to be
determined; it is 27% greater than that of Pluto. Together, its mass
and diameter give its density as 2.52 times that of water, implying
that Eris is probably a rocky body covered in a rather thin mantle of
ice. The surface of Eris appears to be extremely reflective,
reflecting 96% of the light that falls on it (a visible albedo of
0.96 -- brighter even than fresh snow), making Eris one of the most
reflective objects in the Solar System, along with Saturn's icy moon
Enceladus. The bright surface of Eris is most likely composed of a
nitrogen-rich ice mixed with frozen methane, whose presence is
suggested by the spectrum, coating the surface in a thin and very
reflective icy layer less than 1 mm thick. The layer of ice could
result from a nitrogen/methane atmosphere having condensed as frost
onto the surface as Eris moved away from the Sun in its elongated
orbit into an increasingly cold environment. The temperature of the
surface of Eris facing the Sun is estimated to be -238 C at most, and
even lower on the night side. The ice could turn back to gas as Eris
approaches its closest point to the Sun.
COMET STORM IN A NEARBY STAR SYSTEM
NASA
Astronomers using the Spitzer space telescope believe that they see
evidence of an ongoing 'Late Heavy Bombardment' in the 'nearby'
southern-hemisphere star system Eta Corvi, occurring at about the same
stage of formation of a planetary system as in our Solar System.
The Eta Corvi system is approximately one billion years old, which
researchers think is about the right age for such a storm. Some
scientists think that, about 4 billion years ago, about 600 million
years after the Solar System formed, the Kuiper Belt was disturbed by
a migration of Jupiter and Saturn, and that the shift in the Solar
System's gravitational balance scattered the icy bodies in the Kuiper
Belt, ejecting the vast majority into interstellar space and producing
a lot of dust in the belt. Some Kuiper-Belt objects, however, were
set on inward paths that crossed the orbits of the Earth and other
rocky planets. The resulting bombardment of comets lasted until 3.8
billion years ago. The barrage scarred our Moon and produced large
amounts of dust. Spitzer has observed around Eta Corvi a band of dust
whose spectrum resembles that of the Almahata Sitta meteorite, which
fell to Earth in fragments across Sudan in 2008. It is tempting to
imagine that the Eta Corvi dust band represents the remnants of an
obliterated giant comet, which might have been destroyed by a
collision with a planet or some other large body. The dust is located
close enough to Eta Corvi that Earth-like planets could exist in the
collision zone. A second, more massive ring of colder dust located
further out in the Eta Corvi system could be interpreted as a
reservoir of cometary bodies. That ring, discovered in 2005, matches
the size of the region in the Solar System known as the Kuiper Belt,
where icy and rocky left-overs from planet-formation linger. The
comets of Eta Corvi, and the Almahata Sitta meteorite, may have each
originated in the Kuiper Belts of their respective star systems.
BLUE STRAGGLERS IN NGC 188
Northwestern University
A consortium of astronomers led from Wyoming has published a study of
the old open star cluster NGC 188, which is to be found in Cepheus
only 5° from the celestial North Pole. The cluster has around 3,000
stars, all about the same age. In the ordinary course of their
evolution, stars burn out, starting from the brightest and most
massive ones which burn up their hydrogen much more quickly than those
of modest mass. In most cases they finish up by ejecting much of
their mass, leaving behind the compact stellar core as a white dwarf.
In NGC 188, as in many other clusters, we see a few stars that seem
anomalously young, blue and bright, ones that according to the age of
the cluster ought to have burnt up and become white dwarfs by now.
They are known as 'blue stragglers', and are unusually abundant in
NGC 188, which includes 21 of them. It was recognised in the 1960s by
W. H. (later Sir William) McCrea that blue stragglers arise from
binary-star systems in which the less-massive star collects the
expelled envelope of its companion in the final stages of the latter's
evolution, and thereby becomes an object that is more massive -- and
accordingly burns brighter and bluer -- than any of the stars that are
evolving normally as single objects in the cluster. The stripped core
of the formerly more-massive star remains as a white dwarf, still in
orbit with the rejuvenated blue straggler. The orbital periods are
typically of the order of 1000 days. The white-dwarf components of
the binaries are not actually detectable directly, being very faint,
but their existence is manifested by the orbital motion of their blue-
straggler companions.
Much of the NGC 188 data set was collected during the last decade by
the 3.5-m WIYN Telescope on Kitt Peak in Arizona, but a considerable
part was supplied from the Dominion Astrophysical Observatory in
Victoria, B.C., and a contribution was subscribed by the moderator of
these Bulletins from observations that he made in collaboration with
J. E. Gunn with their own radial-velocity spectrometer on the Palomar
200-inch reflector in the 1970s.
ANCIENT SUPERNOVA MYSTERY SOLVED
NASA
In 185 AD Chinese astronomers noted a "guest star" that appeared
in the sky and stayed for about 8 months. By the 1960s, scientists had
recognized that the object was the first documented supernova. Later,
they pinpointed its remnant, called RCW 86, located about 8,000
light-years away. The spherical remains, which cover an area of sky
larger than the Full Moon (and can be viewed online at
http://go.nasa.gov/pnv6Oy ) are larger than expected. New infrared
observations made with Spitzer space telescope and other instruments
indicate that the event was a 'Type Ia' supernova, created by the
relatively peaceful death of a star like our Sun, which then shrank to
become a white dwarf. The white dwarf is thought to have blown up
later as a supernova after siphoning matter from a nearby star. The
observations also show for the first time that a white dwarf can
create a cavity around it before blowing up in a Type Ia event.
A cavity would explain why the remains of RCW 86 are so big. When
the explosion occurred, the ejected material would have travelled
unimpeded by gas and dust and spread out quickly.
VISTA FINDS NEW GLOBULAR CLUSTERS
ESO
Two previously unknown globular clusters were found in new images from
ESO's VISTA survey telescope, adding to the total of 158 known
globular clusters in our Milky Way. The two faint clusters are known
as VVV CL001 and VVV CL002. This small and faint grouping may also be
the globular clusters that are the closest known to the centre of the
Milky Way. As well as globular clusters, VISTA is finding many open,
or 'galactic'. clusters, which generally contain fewer, younger, stars
than globular clusters and are far more common. Another newly
announced cluster, VVV CL003, seems to be an open cluster that lies in
the direction of the Galactic centre, but much further away, about
15000 light-years beyond the centre. It is the first such cluster to
be discovered on the far side of the Milky Way. The newly found
clusters are so faint that it is no wonder that they have remained
un-discovered until now. Because of the absorption of visible
starlight by interstellar dust, such objects can be seen only in
infrared light.
HOW MILKY WAY KILLED OFF SATELLITE GALAXIES
RAS
Researchers have noticed for the first time the existence of a new
signature of the birth of the first stars in our Galaxy. More than 12
billion years ago, the intense ultraviolet light from those stars
dispersed the gas of our Galaxy's nearest companions, virtually
putting a halt to their ability to form stars and consigning them to a
dim future. That explains why some galaxies were killed off, while
stars continued to form in more distant objects. The first stars of
the Universe appeared about 150 million years after the Big Bang.
Back then, the hydrogen and helium gas filling the Universe was cold
enough for its atoms to be electrically neutral. As the ultraviolet
light of the first stars propagated through the gas, it broke apart
the proton--electron pairs that make up hydrogen atoms, returning them
to the so-called plasma state in which they existed in the first
moments of the Universe. That process, known as re-ionization, also
resulted in significant heating, which had dramatic consequences --
the gas became so hot that it escaped the weak gravity of the galaxies
of lowest mass, thereby depriving them of the material needed to form
stars.
The process appears to explain the small number and large ages of the
stars seen in the faintest dwarf-galaxy satellites of the Milky Way,
and why galaxies like the Milky Way have so few satellites around
them. The model appears to match observations of our Galaxy and its
neighbourhood and suggests that the first stars of our Galaxy played a
major role in the photo-evaporation of the satellite galaxies' gas.
It is not large nearby galaxies but our own that caused the demise of
its tiny neighbours, evaporating them through its intense radiation.
COMPLEX CARBON COMPOUNDS EXIST THROUGHOUT THE UNIVERSE
University of Hong Kong
Astronomers at the University of Hong Kong have shown that a substance
commonly found throughout the Universe contains a mixture of component
molecules having many carbon atoms in both 'aromatic' (benzene-ring)
and 'aliphatic' (chain-like) arrangements. The compounds are so
complex that their chemical structures resemble those in coal and
petroleum. Since coal and oil are remnants of ancient life, such
matter was thought to arise only from living organisms, but the team's
discovery suggests that complex carbon compounds can be synthesized in
space even in the absence of life forms.
The researchers investigated a set of infrared emissions detected in
stars, interstellar space, and galaxies -- spectral signatures known
as 'unidentified infrared emission features'. The features have been
supposed to come from simple molecules made of carbon and hydrogen
atoms, called polycyclic aromatic hydrocarbon (PAH) molecules. From
observations taken by the Infrared Space Observatory and Spitzer, the
observers show that the spectra cannot be explained by PAH molecules
but must arise from chemical structures that are much more complex.
>From spectra of novae, they show that stars can make such complex
compounds on extremely short time scales (weeks). Not only are stars
producing such matter, but they are also ejecting it into interstellar
space in the form of what astronomers call dust. The work supports
an earlier idea that old stars can act as molecular factories.
Interestingly, the compounds in star dust are somewhat similar to some
found in meteorites, so they must have been present in the early Solar
System, of which many meteorites are thought to be relics.
Bulletin compiled by Clive Down and moderated by Professor Roger Griffin
(c) 2011 the Society for Popular Astronomy

Sunday, 9 October 2011

New observations by the Wide-field Infrared Survey Explorer (WISE) indicate that there are significantly fewer near-Earth asteroids in the mid-size range than previously thought.

WISE scanned the entire celestial sky twice in infrared light between 2010 January and 2011 February. It observed more than 100,000 asteroids in the main belt between Mars and Jupiter, in addition to at least 585 'near-Earth' ones.

It observed in the infrared, detecting objects by their heat rather than by reflected light, and is supposed to have taken a more accurate census of the asteroid population than previous visible-light surveys which were affected by the differing albedos of asteroids.

The WISE data suggest that more than 90% of the largest near-Earth asteroids (1 km or larger), which would have global consequences if they were to strike the Earth, have been found.

It is believed that all near-Earth asteroids as much as 10 kilometres across, as big as the one that is thought to have wiped out the dinosaurs, are now known.

The new estimate for the number of mid-sized near-Earth asteroids, about 20,000, is lower than the 35,000 previously suggested. However, the majority of mid-size asteroids remains to be discovered.